Generally, in a particle beam therapy device, an accelerator for accelerating a charged particle beam to a desired energy is provided. In the accelerator, a high-frequency acceleration cavity including a plurality of electrodes is provided. The particle beam therapy device accelerates the charged particle beam to a desired energy by supplying high frequency power to the electrode provided in the high-frequency acceleration cavity and irradiates an affected part such as a tumor with the accelerated charged particle beam.
However, immediately after the charged particle beam accelerated to constant energy by the accelerator is emitted, a phenomenon called beam spikes in which intensity of the charged particle beam exceeds a target value may occur. The beam spikes easily occur particularly when a charged particle beam with low energy is emitted.